Thank you for the cut and paste history lesson, you should circulate this to every Thai within the country and see what their reaction is to this little snippet of information - you might be very surprised by the reaction from the ordinary Thai who believe Thailand is the centre of the universe and what you're saying is a load of nonsense.
"made up" being the key - ie stolen from others and re-branded as Thai, nearly everything "Thai" has come from Khmer, India, China, Indonesia, Malaysia, Burma etc.